1. Field
This application relates generally to the field of solar energy, and more particularly to solar tracking for solar array systems.
2. Relevant Background
Renewable energy sources are increasingly seen as the solution to meeting growing energy demands while reducing greenhouse gas emissions and dependence on fossil fuels. Government energy policies, advances in renewable energy technology, and increased investment have contributed to rapid growth of many different renewable energy technologies.
Solar energy devices are one of the fastest growing segments of the renewable energy landscape. For example, the amount of world-wide solar power capacity installed in 2013 increased roughly 35% over prior years. In 2013 alone, an estimated 37 Giga-Watts of photovoltaic (“PV”) solar power capacity was added world-wide. Other solar energy technologies that are in use or development include concentrating solar power (“CSP”), solar hot water heating systems, solar food cookers, solar crop dryers, solar distilleries and desalinators, and the like.
Cost is a major driver for renewable energy installations. Because solar energy systems do not use fuel, the costs for solar power systems are dominated by the capital cost of installation and maintenance costs. While the cost of some solar energy technologies such as photovoltaics are declining due to advances in technology and increases in manufacturing scale and sophistication, continuing to reduce capital and maintenance costs is an important driver to competing against other power sources such as nuclear power and fossil fuels.
In solar energy systems, efficiency is an important aspect of useful energy output of the system. For example, commercial PV cells typically have less than 20% conversion efficiency of incident solar energy. Other factors affecting solar energy generation include the amount of incident solar energy at the installation site and incident angle of solar radiation on the solar energy system.
To increase efficiency, it is known to orient a solar energy device in the direction of maximum exposure to the sun's energy throughout the day. This orientation control, known as solar tracking, can increase the energy output throughout a day by approximately 20-40% over a fixed orientation solar energy device. Solar trackers generally track the sun's movement in either a single axis or using two axes. Single axis trackers have one axis of rotation, which may be oriented horizontally, vertically, or tilted at some angle to horizontal, with the tilt angle commonly adjusted based on latitude of the installation. Dual axis trackers are able to follow the sun in both horizontal and vertical directions and therefore provide optimum solar energy output for a solar energy system. However, tracking the sun's movement based on a single axis provides the most benefit over a fixed orientation with approximately 30% in increased output, with the additional axis of tracking providing only another approximately 6% in energy output.
Solar tracking is generally accomplished with either an active or passive control system. Active solar trackers use sensors or pre-determined data to find the current position of the sun, and actively orient the solar device to face the sun (e.g., using motors, gears, and computers). While active trackers can use a known solar position to orient and therefore are not prone to inaccuracy due to fluctuations in solar energy (e.g., passing clouds, etc.), they are generally expensive with regard to both initial installation and in maintenance costs. Passive solar trackers orient a solar energy device using the sun's energy and without the use of motors. Currently, both active and passive solar trackers can be a substantial cost component in a solar energy system. For these reasons, many solar installations are fixed orientation and do not use solar trackers.
Often, solar energy devices are deployed in arrays of panels that may be mounted at a fixed angle facing south (in the northern Hemisphere), or mounted to a frame that rotates to track the sun. For large electric utility or industrial applications, dozens or hundreds of solar panels may be installed in rows of assemblies, where each solar panel assembly is configured to rotate to track the sun. Generally, current tracking systems use rigid structures and drive systems to move a multitude of solar panels in a solar tracking fashion. These systems present challenges in conforming to undulations and variations in the surface they are installed on. Thus, for ground mounted systems, there is a large amount of expensive grading that needs to be performed.